Conventionally, in financial institutions such as banks, character recognition apparatuses that recognize characters in the serial numbers and the like printed on valuable mediums such as banknotes and checks have been used. For example, character recognition of a serial number printed on a banknote, a check number and amount printed on a check is performed, and the obtained result is used in banknote processing and check processing. The character recognition process includes cutting out a character image of every character from an image captured by capturing a character string, extracting a feature amount of the character from the character image, and comparing the extracted feature amount with dictionary data in which feature amount of each character is registered previously.
The characters on the banknotes and checks may have a variety of patterns (designs) printed in the background. The background patterns may adversely affect character recognition, and it may lead to a misrecognition of the characters not being correctly recognized. To provide a solution to this problem, for example, Patent Document 1 discloses a technology for suppressing the adverse effect of the background pattern so that the characters printed with a background pattern can be read from an amount box in a clear band of a check. Exploiting the fact that the background pattern of the amount box is paler than the color of the characters printed in the amount box, the color border between the character and the background pattern is set as a slice level (threshold value), and the image of the amount box is binarized by using the slice level. With this technique, the background pattern can be removed from the image of the amount box and an image that includes only the characters can be obtained. Consequently, character recognition can be performed accurately.
Although it would be ideal to be able to remove only the background pattern from an image including characters and the background pattern, when image processing such as binarizing and filtering is performed on the image, image quality of even a character portion may deteriorate, leading to erroneous character recognition result. Patent Document 2 discloses a technology for avoiding the adverse effect of image processing performed to remove the background pattern. Specifically, it is evaluated, based on distribution of pixel values of the region including only the background pattern, whether the background pattern will affect character recognition. If it is determined that character recognition will not be positively affected, character recognition is performed without performing the image processing for removing the background pattern. Even if it is determined that the background pattern may positively affect character recognition, image processing for removing the background pattern is performed on the original character image, the image obtained after the image processing is evaluated by using pixel information of the background pattern. If it is determined that image processing will have no positive effects, character recognition is performed by using the original character image without performing the image processing for removing the background pattern.